The production of aniline by decarboxylation of aminobenzoic acid is known in principle in the prior art; see for example Per Wiklund et al., Current Organic Synthesis, 2006, 3, 379-402. Stevens et al., Canadian Journal of Chemistry, 1952, 30 (7), 529-540, reports that an aqueous solution of ortho-aminobenzoic acid could be decarboxylated to aniline in the presence of 0.75N sulfuric acid at 100° C. in 6 hours with a yield of 56%. It had previously been reported in MacMaster and Shriner, J. Am. Chem. Soc., 1923, 45 (3), 751-753 that under similar conditions (in boiling water) but in the absence of acid, ortho-aminobenzoic acid was decarboxylated to aniline in 7 hours with a yield of only 27%.
Publications are also found for this purpose in the recent patent literature; see for example WO 2015/124686 A1 and WO 2015/124687 A1. WO 2015/124686 A1 describes the thermal decarboxylation of ortho-aminobenzoic acid in an aqueous medium in the presence of or without catalyst. WO 2015/124687 A1 describes the catalytic decarboxylation by zeolite catalysis in 1-decanol as solvent. Both applications furthermore describe the further conversion of the aniline thus produced to aniline derivatives such as di- and polyamines of the diphenylmethane series and the corresponding isocyanates.
The aminobenzoic acid starting compound can be obtained chemically or preferably by fermentation.
The chemical production of aminobenzoic acid is described in the literature. A suitable synthesis route (with yields >98%) is, for example, the reaction of phthalimide with sodium hypochlorite. Phthalimide can be obtained in turn from phthalic anhydride and ammonia. The whole process is well-known and is described, for example, in Lorz et al., Phthalic Acid and Derivatives in Ullmann's Encyclopedia of Industrial Chemistry, Volume 27, pp. 140-141, Weinheim, Wiley-VCH. An industrial process is also described in the patent literature; see e.g. DE 29 02 978 A1 and EP 0 004 635 A2.
The production by fermentation of aminobenzoic acid is described in the literature. For the production of aminobenzoic acid by fermentation, reference is made by way of example to Balderas-Hemandez, V. E. et al., “Metabolic engineering for improving anthranilate synthesis from glucose in Escherichia coli”, Microb. Cell. Fact. 2009, 8, 19 (doi: 10.118611475-2859-8-19). Publications can also be found in the patent literature for this purpose; see for example the already mentioned applications WO 2015/124686 A1 and WO 2015/124687 A1 and the literature cited therein in each case.
Fermentation processes generally proceed in an aqueous medium and in the case of production of aminobenzoic acid generally afford aqueous solutions (fermentation broths) with a content by mass of aminobenzoic acid in the range from 10.0 g/L to 100 g/L. The approach described in WO 2015/124686 A1, the direct decarboxylation of the aqueous solution of ortho-aminobenzoic acid, optionally after removal of biomass, is certainly not unattractive per se. However, the method described in WO 2015/124686 A1 requires the extraction of aniline formed in the decarboxylation with an organic solvent extraneous to the system (an alcohol, phenol, amide, ether or aromatic hydrocarbon; in particular, 1-dodecanol is emphasized as a suitable solvent), which is associated unavoidably with additional costs and additional purification complexity (separation of aniline from 1-dodecanol).
WO 2015/124687 A1 describes the procedure of decarboxylation inter alia in water or in an organic solvent extraneous to the system, in particular 1-dodecanol, optionally in the mixture with aniline (cf. page 18, lines 28 and 29). The disadvantages outlined previously of the use of an organic solvent extraneous to the system are therefore also relevant to these embodiments of the decarboxylation. In addition, this document also describes the possibility of carrying out the decarboxylation in aniline (without 1-dodecanol; see FIGS. 35 and 37 to 38 and the accompanying text passages), optionally in the presence of 10% by mass water (see FIG. 36 and the accompanying text passages). Although the document makes no explicit reference to the origin of the aniline used, it is obvious to those skilled in the art from the context that it is pure aniline. The description of this method variant however does not go beyond the illustration of the fundamental possibility of such a decarboxylation of aminobenzoic acid from different sources of aniline. Process engineering details for the source and configuration of the feeding of the aniline to be used in the decarboxylation step in a preferably continuously operating industrial scale process are not to be found in the document.
Further improvements in the production of aniline and aniline conversion products by decarboxylation of aminobenzoic acid, particularly obtained by fermentation, therefore would be desirable. In particular, it would be desirable to be able to design the simplest possible method and without using solvent extraneous to the system (such as 1-dodecanol), in order to increase the economic viability of the method and thus to make its use in industrial scale production more attractive. Furthermore, it would be desirable to design improvements to the decarboxylation step so that the purification of the aniline obtained, preferably carried out by distillation, following the decarboxylation, is not difficult or is even simplified.